Electronic devices are typically rated, or characterized, according to certain parameters to which designers refer when selecting devices for particular applications. Non-linear devices, such as diodes, transistors, solid-state switches, and other such types of devices, are being developed to operate in a wide variety of environments and applications using a wide variety of solid-state technologies. The device's static characteristics determine the device's suitability for particular environments and applications.
Electronic device manufacturers rely on device analyzers to test and characterize electronic devices to provide the device's static characteristics. Device analyzers are equipped with tools for a device by applying a test signal from a power source, and measuring selected parameters at the device-under-test (“DUT”). Device analyzers generally use a curve tracer, which measures both voltage and current at the DUT and plots the measured values as current-voltage (“I-V”) curve traces. The power source applies the test signal to the DUT as a series of voltage and/or current levels in what is known as a “sweep.” The sweep may be a voltage sweep or a current sweep over a range from a minimum level to a maximum level (or from a maximum level to a minimum level) depending on which parameter is controlled at the power source, and the voltage and current are measured at the DUT for each level of the test signal at the DUT. For each sweep, a curve representing the measured values is generated.
Devices having two terminals, such as for example, diodes, may be characterized by a single curve in a single sweep, although other tests not involving test signals in sweeps may be performed as well. Devices having more than two terminals may require multiple sweeps to generate multiple curve traces to test conditions involving signals applied to other terminals. Typically, devices comprise a drain terminal and a source terminal and power is typically applied across the drain and source terminal. Other terminals on the device may be used to vary the operation of the device by affecting the voltage and current levels at the drain and source terminals according to voltage and/or current levels applied to the other terminals. Three-terminal devices, which include transistors (based on a wide variety of technologies such as bipolar junctions, field-effect or “FET,” and involving a wide variety of semiconductor materials and configurations such as metallic oxide semiconductors, or “MOS,” FET's) and other switch-like devices, operate using three-terminals. A gate terminal is used to affect the voltage and current at the drain and source terminals, as for example, an on-off switch or as a bias for regulating the voltage and/or current levels. The I-V curve traces generated for three-terminal devices typically appear as a series of curves generated at varying gate signal levels. Curve traces and their utility in characterizing electronic devices are wellknown in the art.
Device analyzers may perform tests and measurements that require subjecting devices to environments involving conditions that approach or even exceed the device's safe operating area (“SOA”). Until recently, the vast majority of electronic devices have been designed for applications involving DC power sources that are relatively low, such as five volts, or even 12 volts or 24 volts. Device analyzers have been generally capable of testing at such environments.
A growing awareness of the need to conserve energy resources has resulted in the development and increasing demand for power devices that are characterized by a high breakdown voltage and capability of high current density. Wide Band Gap Devices such as for example, devices made with GaN (gallium nitride) and SiC (Silicon Carbide), are attracting attention as devices made with materials with high-temperature properties, withstand voltage characteristics, conduction loss, and transient loss. The ability to perform precise measurement of the characteristics of such devices subjected to high voltage and high current is becoming more important and challenging. Testing requirements of such new power devices are exceeding the power capabilities of current device analyzers.
One problem that arises in testing power devices involves subjecting the device to high voltages and high currents that can destroy the device. Some device analyzers are configured to perform pulsed sweeps. The test signal is applied in pulses and voltage/current measurements are made within the period of the pulse to minimize the amount of time the device is subjected to excess current levels. Known device analyzers typically use pulsed test signals with pulse widths that are too long to adequately protect the DUT from self-heating. The pulse widths are also typically fixed and often not known precluding the ability to modify the pulse width for the needs of specific tests or devices. Known device analyzers also typically lack sufficient power capacity to test high power devices at or near their SOA's. While the limitations of known device analyzers are being exposed by the increasing demand for testing high power devices, existing silicon devices are being developed with lower and lower losses further challenging the capabilities of known device analyzers.
Devices are also being developed using new technologies that require testing in wider and wider ranges. For example, the on-resistance of Laterally Diffused Metal Oxide Semiconductors (“LDMOS”) with a trench structure may be less than 1 milliohm. In another example, the saturation voltage of an insulated gate bipolar transistor (“IGBT”) is less than 1V. Reliability testing at high voltage requires obtaining I-V characteristics where the operating point is close to the device's SOA (Safe Operating Area). New device technologies also result in new effects or device behaviors to test for and characterize. For example, GaN devices are subject to a phenomenon known as “current collapse.” In addition, the on-resistance of power devices is becoming more difficult to measure precisely at such high power levels. Such effects or phenomena cannot be measured or studied effectively via I-V curve traces alone. However, many of the devices analyzed by device analyzers with curve tracers are in integrated circuits, and testing is typically automated and performed onwafer. The addition of different apparatuses or complicating test protocols for characterizing devices would adversely affect the development and manufacturing cycle.
In view of the foregoing, there is an ongoing need for device analyzers having sufficient power capacity to generate I-V characteristics, and to efficiently perform other types of measurements for high power devices at or above their SOAs without damaging the DUT.